For two days, maths became a priority at London Zoo. Here, according to tradition, the new year begins with counting pets. Keepers are armed with notepads and pens and are available to search for animals. Large zoo inhabitants are the easiest to count. For example, all Sumatran tigers are visible at once. There are four of them: Asim and Gaisha, as well as their children Zach and Crispin. There are...